Modulation-type discrimination in a wireless communication network

ABSTRACT

A radio frequency receiver for discriminating a modulation type to decode a signal field of an encoded signal in a wireless communication system. The radio frequency (RF) receiver receives an encoded signal having a preamble training sequence associated with a frame, the preamble training sequence including the signal field. The radio frequency receive generates at least a first log-likelihood ratio (LLR) stream and a second LLR stream for each of a plurality of sub-symbols for a predetermined portion of the received encoded signal based upon an m-bit wide modulation reference, wherein m represents the bit width of the modulation reference. The first LLR stream and the second LLR stream each include a plurality of LLR values. The plurality of LLR values of the first LLR stream are summed to produce a first cumulative LLR, and the plurality of LLR values of the second LLR stream are summed to produce a second cumulative LLR. The first cumulative LLR is discriminated with the second cumulative LLR to produce a discriminated modulation type output. The receiver decodes the signal field based on the discriminated modulation type output.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Application Ser.No. 60/864,532, filed Nov. 6, 2006, and is a continuation-in-part ofU.S. Application No. 11/406,667, filed Apr. 19, 2006, each of which arehereby incorporated herein by reference in their entirety for allpurposes.

BACKGROUND

1. Technical Field

The present invention relates to wireless communications and, moreparticularly, modulation type discrimination for a receivedcommunication signal.

2. Related Art

Communication systems are known to support wireless and wire linedcommunications between wireless and/or wire lined communication devices.Such communication systems range from national and/or internationalcellular telephone systems to the Internet to point-to-point in-homewireless networks. Each type of communication system is constructed, andhence operates, in accordance with one or more communication standards.For instance, wireless communication systems may operate in accordancewith one or more standards, including, but not limited to, IEEE 802.11,Bluetooth, advanced mobile phone services (AMPS), digital AMPS, globalsystem for mobile communications (GSM), code division multiple access(CDMA), local multi-point distribution systems (LMDS),multi-channel-multi-point distribution systems (MMDS), and/or variationsthereof.

Depending on the type of wireless communication system, a wirelesscommunication device, such as a cellular telephone, two-way radio,personal digital assistant (PDA), personal computer (PC), laptopcomputer, home entertainment equipment, etc., communicates directly orindirectly with other wireless communication devices. For directcommunications (also known as point-to-point communications), theparticipating wireless communication devices tune their receivers andtransmitters to the same channel or channels (for example, one of aplurality of radio frequency (RF) carriers of the wireless communicationsystem) and communicate over that channel(s). For indirect wirelesscommunications, each wireless communication device communicates directlywith an associated base station (for example, for cellular services)and/or an associated access point (for example, for an in-home orin-building wireless network) via an assigned channel. To complete acommunication connection between the wireless communication devices, theassociated base stations and/or associated access points communicatewith each other directly, via a system controller, via a public switchtelephone network (PSTN), via the Internet, and/or via some other widearea network.

Each wireless communication device includes a built-in radio transceiver(that is, receiver and transmitter) or is coupled to an associated radiotransceiver (for example, a station for in-home and/or in-buildingwireless communication networks, RF modem, etc.). As is known, thetransmitter includes a data modulation stage, one or more intermediatefrequency stages, and a power amplifier stage. The data modulation stageconverts raw data into baseband signals in accordance with theparticular wireless communication standard. The one or more intermediatefrequency stages mix the baseband signals with one or more localoscillations to produce RF signals. The power amplifier stage amplifiesthe RF signals prior to transmission via an antenna.

An issue that exists for digital receivers is to have the capability ofreceiving various frame formats with different data structures. Often, atransmitter will adjust the transmission modulation-type to one of manybased upon a number of considerations, such as signal interferencelevels, data rate, etc. A receiver, however, does not have a prioriknowledge of the modulation-type of the pertinent portion of a receiveddata frame—that is, knowledge of the modulation-type is not self-evidentor capable of being determined without examination of the receivedsignal. Thus, a need exists for discriminating modulation types of thereceived data frame in view of various frame formats supportingdiffering data throughput to allow the receiver to properly decode ordecipher an incoming signal.

SUMMARY

The present invention is directed to apparatus and methods of operationthat are further described in the following Brief Description of theDrawings, the Detailed Description of the Drawings, and the claims.Other features and advantages of the present invention will becomeapparent from the following detailed description of the invention madewith reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the present invention can be obtained when thefollowing detailed description of the preferred embodiment is consideredwith the following drawings, in which:

FIG. 1 is a functional block diagram illustrating a communication systemthat includes a plurality of base stations or access points, a pluralityof wireless communication devices, and a network hardware component;

FIG. 2 is a schematic block diagram illustrating a wirelesscommunication device that includes the host device, provided by a hostdevice and an associated radio, according to an embodiment of theinvention;

FIG. 3 is a schematic block diagram illustrating a wirelesscommunication device that includes a host device and an associated radioaccording to an embodiment of the invention;

FIG. 4 is a functional block diagram of a digital receiver moduleaccording to an embodiment of the invention;

FIG. 5 illustrates frame formats of encoded signals having signal fieldswith varying modulation types according to an embodiment of theinvention;

FIG. 6 illustrates frame formats of encoded signals using apredetermined portion for modulation-type discrimination according to anembodiment of the invention;

FIG. 7 illustrates other frame formats of encoded signals using a secondpredetermined portion for modulation-type discrimination according to anembodiment of the invention;

FIG. 8 is a block diagram of a modulation-type discriminator accordingto an embodiment of the invention;

FIG. 9 is a table illustrating the operation of the discriminator moduleof FIG. 6;

FIG. 10 is a logic diagram illustrating a method of discriminating amodulation type for a signal field according to an embodiment of theinvention;

FIG. 11 is a simplified block diagram of the digital receiver moduleaccording to an embodiment of the invention;

FIG. 12 is a block diagram of a modulation-type discriminator accordingto an embodiment of the invention;

FIG. 13 is an illustration of a modulation reference constellationaccording to an embodiment of the invention;

FIG. 14 illustrates an example of BPSK modulation discriminationaccording to an embodiment of the invention;

FIG. 15 illustrates an example of rotated-BPSK modulation discriminationaccording to an embodiment of the invention;

FIG. 16 illustrates an example of QPSK modulation discriminationaccording to an embodiment of the invention;

FIG. 17 is a result table illustrating the operation functional state ofthe modulation-type discriminator of FIG. 12; and

FIG. 18 is a logic diagram illustrating a method of discriminating amodulation type according to an embodiment of the invention; and

FIG. 19 is a logic diagram further illustrating to discriminating themodulation-type with the cumulative LLRs of FIG. 18; and

FIG. 20 is a logic diagram illustrating a yet another method fordecoding a signal field of an encoded signal in a wireless communicationsystem according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

The embodiments provided may be practiced in a variety of settings thatimplement a modulation-type discrimination of a signal field via apredetermined portion (for example, the signal field, a portion of thedata packet, et cetera) of a received encoded signal, such as in awireless LAN or other packet-based data networks.

For example, a transmitter transmits an encoded signal having a preambletraining sequence that is associated with a data packet. The encodedsignal is made up of a plurality of symbols. Generally, theconfiguration settings of the data packet such as length and modulationtype are contained in the signal field, which may be considered a partof the preamble training sequence. Because these configuration settingsare necessary for decoding the data packet, the source station encodesthe signal field using a robust modulation type (for example, binaryphase shift key (“BPSK”), rotated BPSK, quaternary phase shift keying(“QPSK”), et cetera).

Within a wireless LAN environment, various frame formats exist forbackwards compatibility purposes (and have lower data-throughputcharacteristics), as well as those formats for higher data-throughputpurposes. Accordingly, the modulation type of the signal field maydiffer among the various frame formats. Furthermore, the signal fieldportion of one frame format may coincide with the data portion ofanother frame format.

A receiver, having high-throughput capability, receives these encodedsignals, and without a priori knowledge of the underlying frame formatsand modulation scheme of the received encoded signal, must discriminatethe modulation-type of the pertinent portion before decoding thereceived signal. The resulting discriminated modulation-type is used todecode the signal field contents, which are then used for furtherprocessing and/or decoding of the associated data packet, such as by adigital receiver processing module, to provide outbound data for use bya host device.

Generally, the modulation type for an encoded signal and its constituentsymbols may be one of many, and is discriminated through use ofsoft-metric methodologies that present a level of confidence to anestimation of a transmitted symbol. With this understanding, theexamples below are described in reference to discriminating a modulationtype of a received encoded signal. Furthermore, although a variety ofdifferent systems and components may be implemented, a particular systemimplementation is illustrated in FIG. 1.

FIG. 1 is a functional block diagram illustrating a communication system10 that includes a plurality of base stations or access points 12, 14,and 16, a plurality of wireless communication devices 18, 20, 22, 24,26, 28, 30, 32, and a network hardware component 34. The wirelesscommunication devices 18 through 32 may be laptop host computers 18 and26, personal digital assistant hosts 20 and 30, personal computer hosts24 and 32, and/or cellular telephone hosts 22 and 28. The details of thewireless communication devices will be described in greater detail withreference to FIGS. 2 and 3.

The base stations or access points 12 through 16 are operably coupled tothe network hardware component 34 via local area network (LAN)connections 36, 38, and 40. The network hardware component 34, which maybe a router, switch, bridge, modem, system controller, etc., provides awide area network (WAN) connection 42 for the communication system 10.Each of the base stations or access points 12 through 16 has anassociated antenna or antenna array to communicate with the wirelesscommunication devices in its area. Typically, the wireless communicationdevices 18 through 32 register with the particular base station oraccess point 12 through 16 to receive services from the communicationsystem 10. For direct connections (that is, point-to-pointcommunications), wireless communication devices communicate directly viaan allocated channel.

Typically, base stations are used for cellular telephone systems andlike-type systems, while access points are used for in-home orin-building wireless networks. Regardless of the particular type ofcommunication system, each wireless communication device includes abuilt-in radio and/or is coupled to a radio. Any one of the wirelesscommunication devices of FIG. 1 may employ the modulation-typediscriminator of the present invention as is described in greater below.Thus, a wireless communication device (such as those of FIG. 1) having ahigh-throughput data capability that is in communication with one of theother wireless communication device within a basic service set, thereceiver of the device may require discriminating the modulation of thereceived encoded signal to access and process components of the receivedsignal, and in turn, decode the accompanying data packet. Thus,according to one embodiment, PC host 32 includes circuitry and logic forthe described embodiments of a modulation-type discriminator.

FIG. 2 is a schematic block diagram illustrating a wirelesscommunication device that includes a host device (provided by hostdevice 18 through 32), and an associated radio 60. For cellulartelephone hosts, radio 60 is a built-in component. For personal digitalassistant hosts, laptop hosts and/or personal computer hosts, the radio60 may be built-in or an externally coupled component.

As shown, the host device 18 through 32 includes a processing module 50,a memory 52, a radio interface 54, an input interface 58 and an outputinterface 56. The processing module 50 and memory 52 execute thecorresponding instructions that are typically performed by the hostdevice 18 through 32. For example, for a cellular telephone host device,the processing module 50 performs the corresponding communicationfunctions in accordance with its particular cellular telephone standard.

The radio interface 54 data can be received from and sent to the radio60. For data received from the radio 60 (for example, inbound data), theradio interface 54 provides the data to the processing module 50 forfurther processing and/or routing to the output interface 56. The outputinterface 56 provides connectivity to an output device such as adisplay, monitor, speakers, etc., such that the received data may bedisplayed. The radio interface 54 also provides data from the processingmodule 50 to the radio 60. The processing module 50 may receive theoutput data from an input device, such as a keyboard, keypad,microphone, etc., via the input interface 58 or generate the dataitself. For data received via the input interface 58, the processingmodule 50 may perform a corresponding host function on the data and/orroute it to the radio 60 via the radio interface 54.

Radio 60 includes a receive signal path circuitry and transmit signalpath circuitry. The receive signal path circuitry includes the digitalreceiver processing module 302 and a receive component 79. The receivefront-end 79 includes an analog-to-digital converter (ADC) 66, afiltering/gain module 68, a down-conversion module 70, a low noiseamplifier 72, and a receive (Rx) filter module 71. The transmit signalpath circuitry includes a digital transmitter processing module 76 and atransmit front-end 77. The transmit front-end 77 includes adigital-to-analog converter (DAC) 78, a filtering/gain module 80, anintermediate frequency (IF) mixing up-conversion module 82, a poweramplifier (PA) 84, and a transmit (Tx) filter module 85. Also includedwith the radio 60 is a transmitter/receiver (Tx/Rx) switch module 73, alocal oscillation module 74, and a memory 75. The antenna 86 is operablycoupled such that it is shared with the transmit and receive signal pathcircuitry, which is regulated by the Tx/Rx switch module 73. Note thatthe antenna implementation will depend on the particular standard towhich the wireless communication device is compliant.

The digital receiver processing module 302 and the digital transmitterprocessing module 76, in combination with operational instructionsstored in memory 75, execute digital receiver functions and digitaltransmitter functions, respectively. The digital receiver functionsinclude, but are not limited to, demodulation, constellation demapping,decoding and/or descrambling. The digital transmitter functions include,but are not limited to, scrambling, encoding, constellation mapping,and/or modulation. The digital receiver and transmitter processingmodules 302 and 76, respectively, may be implemented using a sharedprocessing device, individual processing devices, or a plurality ofprocessing devices. Such a processing device may be a microprocessor, amicro-controller, a digital signal processor, a micro-computer, acentral processing unit, a field programmable gate array, programmablelogic device, a state machine, logic circuitry, analog circuitry,digital circuitry, and/or any device that manipulates signals (analogand/or digital) based on operational instructions.

Memory 75 may be a single memory device or a plurality of memorydevices. Such a memory device may be a read-only memory (ROM), randomaccess memory (RAM), volatile memory, non-volatile memory, staticmemory, dynamic memory, and/or any device that stores digitalinformation. Note that when the digital receiver processing module 302and/or the digital transmitter processing module 76 implements one ormore of its functions via a state machine, analog circuitry, digitalcircuitry, and/or logic circuitry, the memory storing the correspondingoperational instructions is embedded with the circuitry comprising thestate machine, analog circuitry, digital circuitry, and/or logiccircuitry. Memory 75 stores, and the digital receiver processing module302 and/or the digital transmitter processing module 76 execute,operational instructions corresponding to at least some of the functionsillustrated herein.

In operation, the radio 60 receives outbound data 94 from the hostdevice 18 through 32 via the host interface 62. The host interface 62routes the outbound data 94 to the digital transmitter processing module76, which processes the outbound data 94 in accordance with a particularwireless communication standard specification (for example, IEEE802.11a, IEEE 802.11b, IEEE 802.11g, Bluetooth, etc.) to produce digitaltransmission formatted data 96. The digital transmission formatted data96 will be a digital baseband signal or a digital low IF signal, wherethe low IF signal typically will be in the frequency range of 100kilohertz to a few megahertz.

With respect to the transmit front-end 77, the digital-to-analogconverter 78 converts the digital transmission formatted data 96 fromthe digital domain to the analog domain. The filtering/gain module 80filters and/or adjusts the gain of the analog baseband signal prior toproviding it to the up-conversion module 82. The up-conversion module 82directly converts the analog baseband signal or low IF signal into aradio frequency (RF) signal based on a Tx local oscillation (LO) 83provided by the local oscillation (LO) module 74. The local oscillationmodule 74 is, in one embodiment of the invention, a multi-stage mixer. Apower amplifier 84 amplifies the RF signal to produce the outbound RFsignal 98, which is filtered by the transmitter filter module 85. Theantenna 86 transmits the outbound RF signal 98 to a targeted device,such as a base station, an access point, and/or another wirelesscommunication device.

The receive front-end 79 of the radio 60 receives an inbound RF signal88 via the antenna 86. The inbound RF signal 88 was transmitted by abase station, an access point, or another wireless communication device.

The antenna 86 provides the inbound RF signal 88 to the receiver filtermodule 71 via the Tx/Rx switch module 73, where the Rx filter module 71bandpass-filters the inbound RF signal 88. The Rx filter module 71provides the filtered RF signal to low noise amplifier (LNA) 72, whichamplifies the inbound RF signal 88 to produce an amplified inbound RFsignal. The LNA 72 provides the amplified inbound RF signal to thedown-conversion module 70, which directly converts the amplified inboundRF signal into an inbound low IF signal or baseband signal based on areceiver local oscillation 81 provided by local oscillation module 74.The local oscillation module 74 is, in one embodiment of the invention,a multi-stage mixer as described herein. The down-conversion module 70provides the inbound low IF signal or baseband signal to thefiltering/gain module 68. The filtering/gain module 68 may beimplemented to filter and/or attenuate the inbound low IF signal or theinbound baseband signal to produce a filtered inbound signal.

The ADC 66 converts the filtered inbound data from the analog domain tothe digital domain to produce digital reception formatted data 90. Thedigital receiver processing module 302, decodes, descrambles, demaps,and/or demodulates the digital reception formatted data 90 to recaptureinbound data 92 in accordance with the particular wireless communicationstandard being implemented by the radio 60. The host interface 62provides the recaptured inbound data 92 to the host device 18 through 32via the radio interface 54.

As should be readily appreciated by one of skill in the art, thewireless communication device of FIG. 2 may be implemented using one ormore integrated circuits. For example, the host device may beimplemented by a first integrated circuit, while the digital receiverprocessing module 302, the digital transmitter processing module 76, andthe memory 75, may be implemented on a second integrated circuit, andthe remaining components of the radio 60, less the antenna 86, may beimplemented on a third integrated circuit, to provide an integratedcircuit radio transceiver. As yet another example, the processing module50 of the host device 18 through 32 and the digital receiver processingmodule 302 and the digital transmitter processing module 76 may be acommon processing device implemented on a single integrated circuit.Further, memory 52 and memory 75 may be implemented on a singleintegrated circuit and/or on the same integrated circuit as the commonprocessing modules of the processing modules 50, the digital receiverprocessing module 302, and the digital transmitter processing module 76.

The wireless communication device of FIG. 2 is one that may beimplemented to include either a direct conversion from RF-to-basebandand baseband-to-RF or for a conversion by way of a low intermediatefrequency (IF). Accordingly, the LO module 74 includes circuitry foradjusting an output frequency of a local oscillation signal providedtherefrom. The LO module 74 receives a frequency correction input thatit uses to adjust an output local oscillation signal to produce afrequency corrected local oscillation signal output. While LO module 74,up-conversion module 82 and down-conversion module 70 are implemented toperform direct conversion between baseband and RF, it is understood thatthe principles herein may also be applied readily to systems thatimplement an IF conversion step at a low intermediate frequency.

Within host device 18 through 32, as shown in FIG. 2, multipleapplications for an analog-to-digital converter exist. First, an RF mustbe converted to a digital signal by an analog-to-digital converter, suchas ADC 66, for subsequent processing by the digital receiver processingmodule 302. Additional, however, analog-to-digital converters may alsobe used for providing signal magnitude and phase information logic or toa processing module, such as a front-end processor, for circuitcalibration purposes.

FIG. 3 is a schematic block diagram illustrating a wirelesscommunication device that includes the host device 18-32 and anassociated radio 60. For cellular telephone hosts, the radio 60 is abuilt-in component. For personal digital assistants hosts, laptop hosts,and/or personal computer hosts, the radio 60 may be built-in or anexternally coupled component.

As illustrated, the host device 18-32 includes a processing module 50,memory 52, radio interface 54, input interface 58 and output interface56. The processing module 50 and memory 52 execute the correspondinginstructions that are typically done by the host device. For example,for a cellular telephone host device, the processing module 50 performsthe corresponding communication functions in accordance with aparticular cellular telephone standard.

The radio interface 54 allows data to be received from and sent to theradio 60. For data received from the radio 60 (for example, inbounddata), the radio interface 54 provides the data to the processing module50 for further processing and/or routing to the output interface 56. Theoutput interface 56 provides connectivity to an output display devicesuch as a display, monitor, speakers, etc., such that the received datamay be displayed. The radio interface 54 also provides data from theprocessing module 50 to the radio 60. The processing module 50 mayreceive the outbound data from an input device such as a keyboard,keypad, microphone, etc., via the input interface 58 or generate thedata itself. For data received via the input interface 58, theprocessing module 50 may perform a corresponding host function on thedata and/or route it to the radio 60 via the radio interface 54.

Radio 60 includes a host interface 62, a baseband processing module 100,75, a plurality of radio frequency (RF) transmitters 106-110, atransmit/receive (T/R) module 114, a plurality of antennas 86 a, 86 b,to 86 n, a plurality of RF receivers 118-120, and a local oscillationmodule 74.

The baseband processing module 100, in combination with operationalinstructions stored in memory 75, executes digital receiver functionsand digital transmitter functions, respectively. The digital receiverfunctions include, but are not limited to, digital intermediatefrequency to baseband conversion, demodulation, constellation demapping,decoding, de-interleaving, fast Fourier transform, cyclic prefixremoval, space and time decoding, and/or descrambling. The digitaltransmitter functions include, but are not limited to, scrambling,encoding, interleaving, constellation mapping, modulation, inverse fastFourier transform, cyclic prefix addition, space and time encoding, anddigital baseband to IF conversion. The baseband processing moduleincludes a modulation-type discriminator 220 to discriminate themodulation type of a predetermined portion of the received signal. Themodulation-type discriminator 220 is further described with respect toFIGS. 4 through 10.

The baseband processing module 100 may be implemented using one or moreprocessing devices. Such a processing device may be a microprocessor,micro-controller, digital signal processor, microcomputer, centralprocessing unit, field programmable gate array, programmable logicdevice, state machine, logic circuitry, analog circuitry, digitalcircuitry, and/or any device that manipulates signals (analog and/ordigital) based on operational instructions. The memory 75 may be asingle memory device or a plurality of memory devices. Such a memorydevice may be a read-only memory, random access memory, volatile memory,non-volatile memory, static memory, dynamic memory, flash memory, and/orany device that stores digital information. Note that when the basebandprocessing module 100 implements one or more of its functions via astate machine, analog circuitry, digital circuitry, and/or logiccircuitry, the memory storing the corresponding operational instructionsis embedded with the circuitry comprising the state machine, analogcircuitry, digital circuitry, and/or logic circuitry.

In operation, the radio 60 receives outbound data 94 from the hostdevice via the host interface 62. The baseband processing module 100receives the outbound data 94 and, based on a mode selection signal 102,produces one or more outbound symbol streams 104. The mode selectionsignal 102 will indicate a particular mode of operation that iscompliant with one or more specific modes of the various IEEE 802.11standards. For example, the mode selection signal 102 may indicate afrequency band of 2.4 GHz, a channel bandwidth of 20 or 25 MHz and amaximum bit rate of 54 megabits-per-second. In this general category,the mode selection signal will further indicate a particular rateranging from 1 megabit-per-second to 54 megabits-per-second. Inaddition, the mode selection signal will indicate a particular type ofmodulation, which includes, but is not limited to, Barker CodeModulation, BPSK, QPSK, CCK (“Complementary Code Keying”), 16 QAM(“Quadrature Amplitude Modulation”) and/or 64 QAM. The mode selectionsignal 102 may also include a code rate, a number of coded bits persubcarrier (NBPSC), coded bits per OFDM symbol (NCBPS), and/or data bitsper OFDM symbol (NDBPS). The mode selection signal 102 may also indicatea particular channelization for the corresponding mode that provides achannel number and corresponding center frequency. The mode selectionsignal 102 may further indicate a power spectral density mask value anda number of antennas to be initially used for a MIMO communication.

The baseband processing module 100, based on the mode selection signal102, produces one or more outbound symbol streams 104 from the outbounddata 94. For example, if the mode selection signal 102 indicates that asingle transmit antenna is being utilized for the particular mode thathas been selected, the baseband processing module 100 will produce asingle outbound symbol stream 104. Alternatively, if the mode selectionsignal 102 indicates two, three or four antennas, the basebandprocessing module 100 will produce two, three or four outbound symbolstreams 104 from the outbound data 94.

Depending on the number of outbound symbol streams 104 produced by thebaseband processing module 100, a corresponding number of the RFtransmitters 106-110 will be enabled to convert the outbound symbolstreams 104 into outbound RF signals 112. In general, each of the RFtransmitters 106-110 includes a digital filter and upsampling module, adigital-to-analog conversion module, an analog filter module, afrequency up conversion module, a power amplifier, and a radio frequencybandpass filter. The RF transmitters 106-110 provide the outbound RFsignals 112 to the transmit/receive module 114, which provides eachoutbound RF signal to a corresponding antenna 86 a, 86 b, to 86 n.

When the radio 60 is in the receive mode, the transmit/receive module114 receives one or more inbound RF signals 116 via the antennas 86 a,86 b, to 86 n and provides them to one or more RF receivers 118-122. TheRF receiver 118-122 converts the inbound RF signals 116 into acorresponding number of inbound symbol streams 124. The number ofinbound symbol streams 124 will correspond to the particular mode inwhich the data was received. The baseband processing module 100 convertsthe inbound symbol streams 124 into inbound data 92, which is providedto the host device 18-32 via the host interface 62.

As one of ordinary skill in the art will appreciate, the wirelesscommunication device of FIG. 3 may be implemented using one or moreintegrated circuits. For example, the host device may be implemented ona first integrated circuit, the baseband processing module 100 andmemory 75 may be implemented on a second integrated circuit, and theremaining components of the radio 60, less the antennas 86 a, 86 b, to86 n, may be implemented on a third integrated circuit. As an alternateexample, the radio 60 may be implemented on a single integrated circuit.As yet another example, the processing module 50 of the host device andthe baseband processing module 100 may be a common processing deviceimplemented on a single integrated circuit. Further, the memory 52 andmemory 75 may be implemented on a single integrated circuit and/or onthe same integrated circuit as the common processing modules ofprocessing module 50 and the baseband processing module 100.

FIG. 4 is a functional block diagram of the baseband processing module100 with a receiver path that includes an equalizer 306, ademapper/demux 310, a de-interleave 314, a decode 316, and a descramble318. The demapper/demux 310 includes functional components providing amodulation-type discriminator 220.

The baseband processing module 100 is coupled to receive an RF signalfrom the antenna 86 a, which is representative of the one or moreinbound RF signals 116 via the antennas 86 a, 86 b, to 86 n and providesthem to one or more RF receivers 118-122. For this example, receiver 118is shown. The RF signal was transmitted as an encoded signal having apredetermined portion that utilizes one or several of a plurality ofmodulation types, such as BPSK, rotated BPSK, QPSK, QAM, etc., and wastransmitted over a channel that carries symbols from the transmitter tothe receiver. The channel is serviced by a wired, wireless, optical, oranother media, depending upon the communication system type. Generally,the wireless channel distorts the symbols of the inbound RF signal 116during transmission, from the perspective of the receiver, causinginterference between a subject symbol and a plurality of symbolssurrounding the subject symbol. This type of distortion is referred toas “inter-symbol-interference” and is, generally speaking, thetime-dispersed receipt of multiple copies the symbols caused bymultipath interference. The wireless channel also introduces noise intothe symbols prior to their receipt. The receive path modules areoperable to compensate for these adverse transmission effects andprocess the RF signal 116.

The RF receiver 118 is coupled to provide the received encoded signal asan inbound symbol stream 124 to the equalizer 306. The equalizer 306removes and/or mitigates the channel effects on a received symbol streamof the RF signal. In operation, the equalizer 306 performs channelinversion to produce noisy estimates of the transmitted symbols. In aMIMO system, the equalization process separates out the streams so thateach can be treated independently.

The equalizer 306 output is provided to the demapper/demux 310 thatincludes a modulation-type discriminator 220. The constellationdemapper/demux 310 produces soft metrics (or soft decisions) thatgenerally correlate to the transmitted symbols.

From the demapper/demux 310, the de-interleave 314 serves tode-interleave the output of the demapper/demux 310, placing the data inthe sequence existing prior to the interleaving process by thetransmission source. Generally, an encoded signal will be interleaved ata transmitter, such as under WLAN standards specifications. Thede-interleaved output is provided to the decode 316, which may beprovided as a Viterbi decoder, or other decoder acceptable to thecommunications standards specifications. The decoded bits are thendescrambled at descramble 318. The resulting data bits are output asinbound data 92.

In operation, the RF receiver 118 (or RF receivers 118-122, dependingupon the number of streams) receives an encoded signal in an analog formrepresented as inbound RF signals 116. The encoded signal has a preambletraining sequence associated with a data packet. Further to thisexample, the RF receiver 118 converts the inbound RF signal 116 of theencoded signal into a corresponding inbound symbol stream 124.Generally, the configuration settings of the data packet such as lengthand modulation type are contained in the signal field, which may beconsidered a part of the preamble training sequence. Because theconfiguration settings are necessary for decoding the data packet, thesignal field is always encoded using a robust modulation type (forexample, binary phase shift key, rotated binary phase shift keying,quaternary phase shift keying, et cetera).

Within a wireless LAN environment, various frame formats exist forbackwards compatibility purposes (and lower data-throughputcharacteristics), as well as those formats for higher data-throughputpurposes. Accordingly, the modulation type of the signal field maydiffer among the various frame formats. Furthermore, the signal fieldportion of one frame format may coincide with the data portion ofanother frame format.

A receiver for a radio 60, having high-throughput capability, receivesthese encoded signals, and without a priori knowledge of the underlyingframe formats and modulation scheme of the received encoded signal, mustdiscriminate the modulation-type of the pertinent portion beforedecoding the data portion for the received signal. The receiver uses theresulting discriminated modulation-type to decode the signal fieldcontents, which the receiver then uses for further processing and/ordecoding of the associated data packet of the frame, such as by adigital receiver processing module 302 (see FIG. 2) and/or a basebandprocessing module 100, to provide inbound data 92 for use by a hostdevice 18-32.

Preamble training sequences and structures of the encoded signal arediscussed in further detail with respect to FIGS. 5 and 7. Themodulation-type discriminator 220 determines, or discriminates themodulation type for the signal field at the outset to allow for decodingof the encoded signal and the associated data. The signal fieldspecifies the data configuration and length-related parameters for thedata carried by the encoded signal. Generally, the baseband processor100 performs the reverse operations of a transmitter with trainingoverhead—for example, estimating a frequency offset and the symboltiming with respect to the received encoded signal. The trainingactivity is conducted through use of a preamble training sequence.

FIG. 5 illustrates frame formats of encoded signals. The encoded signals400 are examples of frame formats that may be used within acommunication system 10 (see FIG. 1). Shown is a legacy frame format402, a high-throughput frame format 422 and a high-throughput frameformat 442. The frame formats have at least two components—a preambletraining sequence and a data packet.

Generally, the preamble training sequences contain known trainingsymbols, in accordance with one or more standards specifications, toprovide for estimation of the wireless communication channel. Thepreamble provides sufficient information for packet detection, frequencyoffset estimation, symbol timing, and channel estimation. Furthermore,in WLANs, for example, the preamble training sequence is added to everydata packet 406, 430 and 446 prior to transmission. As part of thesynchronization processes, the preamble training sequence have shorttraining symbols STRN, long training symbols LTRN, and a signal field.In general, the short training symbols STRN (generally about 10 periodsof 0.8 microseconds each in one embodiment of the invention), are usedto detect the start-of-frame, gain control sequence (to place the signalin a range suitable for detection), carrier frequency offset, symbolrecovery, etc. The long training symbol LTRN (for example, in OFDMtechniques, generally having 2 periods of a training symbol each beingfour microseconds) provide information for channel estimation and fineimprovements to receiver performance. The signal fields 408, 433, and449 are modulated, and contain configuration info necessary for decodingthe data packets 406, 430, and 446 respectively.

The frame formats 402, 422, and 442 represent frame formats that may beused in a wireless local area network (WLAN) providing systems withenhanced data capability and throughput. It should be noted, however,that these frame formats are provided as examples, and that other frameformats having a preamble training sequence with data packet structurefor packet-based communications systems may be used.

The legacy frame format 402 has a preamble 404 and a data packet 406.The preamble 404 has a short training sequence STRN 410, a long trainingsequence LTRN 412, and a signal field 408, shown as a legacy signalfield (L-SIG). In general, the legacy frame format 402 illustrates aprevalent format used for data communications. For example, such formatsare used in IEEE 802.11a, which has a maximum raw data rate of 54Mbit/s, which yields realistic “net achievable throughput” in the mid-20Mbit/s.

The high-throughput frame format 422 has a preamble 424 and a datapacket 430. The preamble 424 has a legacy field 426 and ahigh-throughput field 428. The legacy field 426 allows a receiver toreceive these high-throughput frames by legacy devices. The legacy field426 has a short training sequence STRN 431, a long training sequenceLTRN 432, and a legacy signal field (L-SIG) 429. The high-throughputfield 428 has a high-throughput signal field HT-SIG 433, ahigh-throughput short training field HT-STF 434, and a high-throughputlong training field HT-LTF 435.

The high-throughput frame format 442 has a preamble 444 and a datapacket 446. A legacy, or backwards compatible, portion is not present.The preamble 444 has a short training sequence STRN 447, a long trainingsequence LTRN 448, and a signal field 449, shown as a high-throughputsignal field (SIGNAL-N).

The source, or transmitting, station encodes the signal fields of thevarious formats with robust modulation techniques (for example, BPSK,rotated-BPSK, QPSK) to withstand adverse channel effects. Before asignal field for a received frame can be properly decoded, however, thedestination, or receiving, station need to determine the modulation typeof the signal field. Since the destination station lacks a prioriknowledge of the frame format it is receiving, the destination stationneeds to determine, or discriminate, the modulation type of the signalfield on the fly—that is, the discrimination occurs as the signal isbeing received. Since the location of the signal field (legacy orhigh-throughput) for each frame format is in a fixed relation withrespect to the frame structure, having a priori information regardingthe frame structure or formats allows for pre-determining the portion ofthe received frame to discriminate the modulation type for the signalfield.

FIGS. 6 and 7 illustrate predetermined portions of received encodedsignals 500 for modulation-type discrimination and the relation ofdifferent high-throughput frame formats with respect to legacy frameformats. In the example of FIG. 6, provided is a legacy frame format 502and a high-throughput frame format 522. Because the rate field withinthe legacy signal field 529 of the high-throughput frame format 522 willcorrespond to a 6 Mbps data rate in a legacy deployment, an ambiguityarises as to whether the receiver is receiving a legacy frame format 502(such as the 6 Mega bit-per-second frame format) or a high-throughputframe format 522. In a legacy 6 Mbps frame format, the data packet 506is BPSK-encoded. To mitigate the ambiguity between the types of framebeing received, that is, whether the frame is a legacy frame or ahigh-throughput frame, portions of a received encoded signal may bediscriminated apart from those pertaining to the signal field, such assignal fields 508 and 509. For example, the high-throughput signal fieldHT-SIG 533 of the high-throughput frame format 522 generally coincideswith the start of the data packet 506 for the legacy frame format Themodulation of the high-throughput signal field 533 is rotated-BPSK, andthe modulation of the data packet 506 is BPSK. The predetermined portion520 defines the portions of the encoded signals for modulation-typediscrimination between the frame formats 502 and 522. With thediscriminated modulation type, the receiver is operable to access theinformation contained in the signal field 508 of the legacy frame format502 or in the high-throughput signal field 533 of the high-throughputframe format 522.

As noted earlier, the predetermined portion used for modulation-typediscrimination is based upon the frame formats that are used. FIG. 7illustrates the selection of predetermined portions 521 of receivedsignals to distinguish between a high-throughput frame format 542 and alegacy frame format 502.

The high-throughput frame format 542 has a preamble 544 and a datapacket 546. The preamble 544 has a short training sequence STRN 547, along training sequence LTRN 548, and a signal field 549, which is ahigh-throughput signal field (SIGNAL-N). The predetermined portion 521coincides with the QPSK-encoded signal field 549 of the high-throughputframe format 542 and the BPSK-encoded signal field 508 of the legacyframe format 502.

As may be appreciated by one of ordinary skill in the art, a radioreceiver may provide modulation-type discrimination for additional frameformats as well as having the flexibility to accommodate combinations ofpossible frame formats within an encoded signal 500. For example, areceiver may be configured to accommodate the legacy frame format 502and the high-throughput frame format 522 of FIG. 6, provided as a firstset, having a first predetermined portion 520. The high-throughput frameformat 542 and the legacy frame format 502 of FIG. 7 may be provided asa second set, having a second predetermined portion 521. In this regard,the modulation-type discriminator may provide discrimination of themodulation type of the predetermined portion 520 and the predeterminedportion 521 of the first and the second set, respectively, such that thedestination station can discriminate the modulation-type for multipleframe sets. When the modulation type of the predetermined portion ofeither frame format is discriminated, the receiver may discern whichframe format is, or is in the process of being received and subsequentlydecode the data packet. In this manner, the receiver has the capabilityto accommodate high-throughput transmissions, while also providingbackwards-compliant data communications with devices withouthigh-throughput capability.

Also, a further distinction between the first predetermined portion 520and the second predetermined portion 521 for a received encoded signalmay be made through pre-processing activity, as may be appreciated byone of ordinary skill in the art, within the MAC Layer by aMedia-specific Access Control (MAC) processor, which may be implementedby the baseband processing module 100. As technological improvementsadvance with respect to hardware and software speed and power,communications standards specifications are generated or amended toincrease data throughput, among other improvements, to communicationssystems.

It should be noted, however, that the frame formats of FIGS. 6 and 7 areprovided as examples, and that other frame formats having a preambletraining sequence with data packet structure for other packet-basedcommunications systems may be used. For example, additional structuresmay be implemented, such as a mid-amble, which may contain a trainingsequence whose configuration depends on the modulation format used.

Further, as one of ordinary skill in the art will appreciate, themodulation-type discrimination techniques for the frame formats (such asthose shown in FIGS. 5 and 6) may be used in the receive signal paths ofa variety of network topologies, such single-input, single output(SISO), multiple-input, multiple-output (MIMO), single-input,multiple-output (SIMO), etc. Each of these topologies has differingadvantages and applications with respect to the wireless transmissionenvironment for a radio link. Also, various transmitter and receivertechniques may be deployed, for example, signal carrier techniques suchas BPSK, multiple carrier techniques such as a QPSK, etc.

For example, with respect to WLAN communications systems, datathroughput of at least 100 Mbit/s is achievable using at least in partMIMO topologies in which the throughput rate is generally four-to-fivetimes faster than under IEEE 802.11a or 802.11g, and perhaps twentytimes faster than under IEEE 802.11b. MIMO communication techniques makeuse of multi-element antenna arrays at both the transmit and the receiveside of a radio link. For further comparison, MIMO communicationtechniques also improve throughput capacity over single-inputmultiple-output (SIMO) systems. SIMO channels in wireless networks canprovide diversity gain, array gain, and interference canceling gainamong other benefits. In addition to these advantages, MIMO links canoffer a multiplexing gain by opening N_(min) parallel spatial channels,where N_(min) is the minimum of the number of transmit and receiveantennas.

With such improvements, legacy system interoperability with legacy frameformats is also needed while supporting these improved throughputtechnologies. Interoperability provides support for various frameformats while achieving the objectives of improved data transmission fora communications system. The legacy frame format 402 represents a formatused in legacy-based communications systems. The frame formats 422 and442 represent frame formats for use in communications systems havingimproved throughput.

Notably, receiver signal path circuitry such as that in FIG. 4 has no apriori knowledge about packet-arrival times, modulation, or encryptionof the received encoded signal. Generally, it is unreasonable to assumethat a receiver has prior knowledge of a time-varying channel, where innoncoherent communications, the receiver must estimate both the channeland the data. The random nature of the arrival times and the high datathroughput require the synchronization to be completed shortly after thestart of the reception of a frame, which is processed using observedcharacteristics or processed a posteriori.

FIG. 8 is a block diagram of a modulation-type discriminator 220 thatincludes a weighted combiner module 222, and a discriminator module 226.The modulation-type discriminator 220 is operable to receive apredetermined portion of an encoded signal 500 (see FIGS. 6 and 7). Thepredetermined portion of the inbound symbol stream 124 may be providedas a predetermined portion 520 and/or 521 of FIGS. 6 and 7. The encodedsignal 500 has a preamble training sequence associated with a datapacket. A predetermined portion of the encoded signal has a plurality ofsymbols x that are encoded in one of a plurality of modulation types.

The equalizer 306 transforms the symbols x of the predetermined portionof the received signal in such a way that the soft metrics that make upthe soft-metric streams 223(1) and 223(2) used by the modulation-typediscriminator 220 are represented by the real and imaginary parts ofeach of the equalized symbols x. That is, the streams are represented ina quadrature or complex form for quadrature processing. The weightedcombiner module 222 receives the plurality of soft metric streams 223(1)and 223(2) and operates to cumulatively sum the soft metrics containedin each of the plurality of soft metric streams to produce cumulativesoft metrics 224(1) and 224(2). The discriminator module 226 is operableto receive the cumulative soft metrics 224(1) and 224(2), and is furtheroperable to compare the cumulative soft metrics 224(1) and 224(2) toprovide a discriminated modulation type from the plurality of specifiedmodulation types. The discriminated modulation type is provided to themodulation type output 228.

For the example provided, the specified modulation types represented inFIGS. 6 and 7 are BPSK, rotated BPSK, and QPSK. As should be readilyappreciated by those skilled in the art, additional specified modulationtypes can be provided with respect to further development or classeswith respect to the encoded signals 400.

The discrimination is made for robust modulation types that exhibittransmission tolerance in view of environmental factors (for example,signal interference, attenuation, etc.). Examples of robustmodulation-types are QPSK, BPSK, and rotated-BPSK BPSK is a method ofencoding and/or transmitting on top of a carrier. The basic principlebehind BPSK is to provide a carrier whose phase is alternated between0-degrees and 180-degrees, as needed, to convey digital information.Rotated BPSK provides a phase that is alternated between 90-degrees and270 degrees. QPSK is a form of modulation in which a carrier sends datasymbols using a four phase modulation scheme to reflect one of fourdifferent two-bit wide data signals (00, 01, 10 and 11). Those phasestypically are 45, 135, 225, and 315 degrees. The change in phase fromone symbol to the next encodes two bits per symbol. In QPSK, the fourangles are usually out of phase by ninety degrees.

As an example, from the inbound symbol stream 124, there are N symbolsin the predetermined portion (for example, predetermined portion 521 orthe predetermined portion 520). Let e_(k), where k is the symbol number,denote the equalized output of these N symbols. Then soft-metric stream223(1) is made up of the real part of each equalized symbol e_(k),

-   -   Soft-metric stream 223(1)=Re(e_(k)), where k=1, . . . , N and        soft-metric stream 223(2) is made up of the imaginary part of        each equalized symbol e_(k)    -   Soft-metric stream 223(1)=Im(e_(k)), where k=1, . . . , N        The cumulative values 224(1) and 224(2) are then formed by        summing the absolute value of each component of soft-metric        streams 223(1) and 223(2) respectively.        ${{Cumulative\_ soft}{\_ metric}\_ 224(1)} = {\sum\limits_{k = 1}^{N}{{{Re}\left( e_{k} \right)}}}$        ${{Cumulative\_ soft}{\_ metric}\_ 224(2)} = {\sum\limits_{k = 1}^{N}{{{Im}\left( e_{k} \right)}}}$        If the N symbols of the predetermined portion of the inbound        symbol stream 124 are encoded using BPSK, then the cumulative        soft metric 224(1) will be much larger than the cumulative soft        metric 224(2). This may be represented as:        Cumulative_soft_metric_(—)224(1)>Cumulative_soft_metric_(—)224(2)        Accordingly, the a posteriori likelihood is that the modulation        type output 228 is BPSK.

If the N symbols of the predetermined portion of the inbound symbolstream 124 are encoded using rotated-BPSK, then the cumulative softmetric 224(1) will be much smaller than the cumulative soft metric224(2). This may be represented as:Cumulative_soft_metric_(—)224(1)<Cumulative_soft_metric_(—)224(2)Accordingly, the a posteriori likelihood is that the modulation typeoutput 228 is rotated-BPSK.

If the N symbols of the predetermined portion 229 are encoded usingQPSK, then the cumulative soft metric 224(1) is substantially equivalentto the cumulative soft metric 224(2). This relationship may berepresented as:Cumulative_soft_metric_(—)224(1)≈Cumulative_soft_metric_(—)224(2)Accordingly, the a posteriori likelihood is that the modulation typeoutput 228 is QPSK.

FIG. 9 is a table illustrating the operation functional state of themodulation-type discriminator 220 of FIG. 8. As shown, the table 700 hasthree columns, a comparison results 225 column, a cumulative soft metric224 column, and a modulation type 228 column.

The table is divided into a favorable column and an unfavorable columnwith respect to designation and modulation types 228. The arrangement ofthe table is informational in that it does not set out a mandatedcomparison sequence or order. For example, the magnitude differencesshown in rows 704 and 706 are more readily discernible with respect tothe magnitude of the difference shown in row 702. It follows then thatif the conditions set out in rows 704 and 706 do not exist, then thelogical result is a favorable comparison result of row 702. As should bereadily appreciated by those skilled in the art, other comparisonmethodologies may be used for arriving at a modulation-type outputdecision. Two cumulative soft metrics 224(1) and 224(2) (see FIG. 7) aregenerated. With respect to row 702, a favorable result with respect tocumulative soft metrics is provided when the first cumulative softmetric 224(1) is substantially equivalent to the second cumulative softmetric 224(2). In other words, the modulation-type of the signal fieldfrom the received encoded signal correlates to a QPSK modulation type.

With respect to row 704, an unfavorable result exists when the firstcumulative value 224(1) is greater than the second cumulative value224(2) scaled by a tolerance 13, which indicates a BPSK modulation type.As should be readily appreciated by those skilled in the art, atolerance “β” may be provided to take into consideration variances,channel characteristics, and/or other factors influencing the receivedsignal. For example, a large number of variants are introduced throughthe transmission environment, the a posteriori likelihood can be madegreater by placing the tolerance β greater than “1.”

In the third row designated as row 706, a further unfavorabledetermination is made where the first cumulative value 224(1) is lessthan the second cumulative value 224(2) scaled by a tolerance β. In thisinstance, the modulation type 228 for the predetermined portion is arotated-BPSK. Again, for example, a large number of variants areintroduced through the transmission environment, the a posteriorilikelihood can be made greater by placing the tolerance “β” less than“1.”

FIG. 10 is a logic diagram illustrating a method of discriminating amodulation type. Starting at step 802, the method 800 proceeds to step804 where an encoded signal is received. At step 806, cumulative valuesare generated from soft metrics, which may be provided by an equalizer(see FIG. 8), through demapping, or other suitable form of soft metricgeneration. Proceeding to step 808, the modulation type is discriminatedby comparing the cumulative values generated in step 806. At step 810, adetermination is made of whether a favorable comparison is achieved.When a favorable comparison results, then in step 812 set the modulationtype of the signal field for the encoded signal to a first specifiedmodulation type of a plurality of specified modulation types. When anunfavorable comparison results, then in step 814, set the modulationtype to one of a second or a third specified modulation type. Followingsteps 812 and 814, at step 816, the method conducts a decoding of thesignal field based on the discriminated modulation type. As should benoted, the process continues with respect to each of the encoded signals400 that may be received by the radio 60.

FIG. 11 is a simplified block diagram of the digital receiver module302. The digital receiver processing module 302 includes an equalizer306, a demapper/demux 310, a de-interleave 314, a decode 316, and adescramble 318. The demapper/demux 310 includes functional componentsproviding a modulation-type discriminator 820 to discriminate themodulation-type of received signals.

The baseband processing module 100 is coupled to receive an RF signalfrom the antenna 86, in which the RF signal was transmitted as anencoded signal having a predetermined portion that utilizes one orseveral of a plurality of modulation types, such as BPSK (Binary PhaseShift Keying), rotated BPSK, QPSK (Quaternary Phase Shift Keying), QAM(Quadrature Amplitude Modulation), et cetera.

The RF receiver 118 outputs an inbound symbol stream 124, which isprovided to the constellation demapper/demux 310, which includes amodulation-type discriminator 820 to discriminate the modulation type ofthe inbound symbol stream 124. The constellation demapper/demux 310produces log-likelihood ratio (“LLR”) streams 822, which include aplurality of soft metrics (or soft decisions) that generally correlateto the received symbols. The modulation-type discriminator 820 isdiscussed in detail with respect to FIG. 12.

From the constellation demapper/demux 310, the de-interleave 314receives and de-interleaves the LLR streams 822. Generally, an encodedsignal will be interleaved by a transmitter per applicable standardsspecifications (such as IEEE 802.11). Interleaving avoids long runs of“zeros” and “ones.”. The de-interleaved streams are decoded at decode316, which may be provided as a Viterbi decoder, or other decoders asmay be specified in the applicable standards specification. The decodedbits are then descrambled at descramble 318. The resulting data bits areoutput as inbound data 92.

In operation, the RF receiver 118 receives inbound RF signals 116 havinga frame format that includes a preamble training sequence associatedwith a data packet. Generally, the configuration settings of the datapacket such as length and modulation type are contained in a signalfield, which may be considered a part of the preamble training sequence.Because the configuration settings are necessary for decoding the datapacket, the signal field is encoded using a robust modulation type (forexample, binary phase shift key, rotated binary phase shift keying,quaternary phase shift keying, et cetera).

Within a wireless communication environment, various frame formats existfor backwards compatibility purposes (and lower data-throughputcharacteristics), as well as those formats for higher data-throughputpurposes. Accordingly, the modulation type of the signal field maydiffer among the various frame formats. Furthermore, the signal fieldportion of one frame format may coincide with the data portion ofanother frame format, such as the frame formats described in FIGS. 5through 7.

The radio 60, having high-throughput data capability, receives theseinbound RF signals 116, and without a priori knowledge of the underlyingframe formats and modulation schemes, must discriminate themodulation-type of the pertinent portion before decoding the dataportion for the received signal. The receiver uses the resultingdiscriminated modulation-type to decode the signal field contents, whichthe receiver uses to process and/or decode the associated data packet ofthe frame via the baseband processing module 100 (or the digitalreceiver processing module 302 of FIG. 2) to produce inbound data 92 tothe host device 18-32.

The modulation-type discriminator 820 initially determines, ordiscriminates the modulation type for the signal field to allow fordecoding of the encoded signal and the associated data. The signal fieldspecifies the data configuration and length-related parameters for thedata carried by the encoded signal. Generally, the baseband processor100 performs the reverse operations of a transmitter with trainingoverhead—for example, estimating a frequency offset and the symboltiming with respect to the received encoded signal. The trainingactivity is conducted through use of a preamble training sequence.

FIG. 12 is a block diagram of a modulation-type discriminator 820 thatincludes an LLR (log-likelihood ratio) computation module 821, a summingmodule 824, and a discriminator module 828.

The LLR computation module 821 receives, via the equalizer 306, apredetermined portion 520 (see FIG. 6) or 521 (see FIG. 7) of the frameformats for the inbound symbol stream 124. The predetermined portion ofthe inbound symbol stream 124 includes a plurality of symbols x that areencoded in one a plurality of modulation types (such as BPSK, QPSK, etcetera).

The LLR computation module 821 generates a plurality of LLR streams 822based upon generating an LLR value for each bit of the plurality ofsymbols x with respect to a modulation reference 836. The modulationreference 836 is an m-bit wide signal reference. For example, when themodulation reference 836 is a two-bit wide signal reference with m equalto two (such as with a QPSK reference), then the LLR computation module821 produces two LLR streams 822. In this example, the specifiedmodulation types, presented in FIGS. 6 and 7, are BPSK, rotated BPSK,and QPSK. As should be readily appreciated by those skilled in the art,additional specified modulation types can be provided with respect tofurther development or classes with respect to the frame formats for theinbound RF signals 116.

The summing module 824 receives the plurality of LLR streams 822(1)through 822(m) from the LLR computation module 821, and sums theplurality of LLR values of the respective LLR stream 822(1) through822(m) to produce cumulative LLRs 826(1) through 826(m). Thediscriminator module 828 receives the cumulative LLRs 826(1) through826(m) and compares the cumulative LLRs 826 to provide a modulation typeoutput 830 from the plurality of specified modulation types.

In operation, the modulation-type discriminator 820 computes thelog-likelihood ratio of each bit of the plurality of symbols x from thepredetermined portion 520 (or 521) of the inbound symbol stream 124.Because each symbol is presumed to be m-bits wide, the LLR computationmodule 821 generates a plurality of LLR streams 822(1), 822(2), . . . ,822(m). In general, the LLR bit b_(i) is provided by the a posterioriprobability ratio (APPR), which can be represented by: $\begin{matrix}\begin{matrix}{{APPR}_{\quad i} = {\log\frac{P\left( \quad{b_{\quad i}\quad = \quad\left. 1\quad \middle| \quad r \right.} \right)}{P\left( \quad{b_{\quad i}\quad = \quad\left. 0\quad \middle| \quad r \right.} \right)}}} \\{= {\log\frac{\sum\limits_{\hat{s} \in S_{i}^{-}}{P\left( \hat{s} \middle| r \right)}}{\sum\limits_{s \in S_{i}^{-}}{P\left( \hat{s} \middle| r \right)}}}} \\{= {\log\frac{\sum\limits_{\hat{s} \in S_{i}^{+}}{{P\left( r \middle| \hat{s} \right)}{P\left( \hat{s} \right)}}}{\sum\limits_{\hat{s} \in S_{i}^{-}}{{P\left( r \middle| \hat{s} \right)}{P\left( \hat{s} \right)}}}}}\end{matrix} & \lbrack a\rbrack\end{matrix}$where “r” is the received symbol and can be represented mathematicallyas r=hs+n, with h denoting the channel and n denoting the additive whiteGaussian noise; Ŝ is the candidate transmit symbol with a bit mapping of{b₀, b₁, . . . }, S_(i) ⁺ is the set of transmit symbols where b_(i)=1;and S_(i) ⁻ is the set of transmit symbols where b_(i)=0.

Generally, if the log ratio given by formula [a] is positive, then ahigher confidence that the ^(ith) bit is a “1” than a “0.” On the otherhand, if the log ratio given by formula [d] is negative, then there is ahigher confidence of the ^(ith) bit being a “0” than a “1.” The morepositive or negative the log ratio is, the higher the confidence of thecorresponding estimate.

With no a priori knowledge, the APPR_(i), the ratio of sums ofprobability, is: $\begin{matrix}{{APPR}_{i} = {{LLR}_{i} = \frac{\sum\limits_{s \in S_{i}^{+}}{P\left( r \middle| \hat{s} \right)}}{\sum\limits_{s \in S_{i}^{-}}{P\left( r \middle| \hat{s} \right)}}}} & \lbrack b\rbrack\end{matrix}$where p(r|ŝ) is given by: $\begin{matrix}{{p\left( r \middle| \hat{s} \right)} = {\frac{1}{{\pi\sigma}_{n}^{2}}{\mathbb{e}}^{{- \frac{1}{\sigma_{n}^{2}}}{{r - {h\quad\hat{s}}}}^{2}}}} & \lbrack c\rbrack\end{matrix}$Using the nearest-neighbor approximation, LLR_(i) becomes:$\begin{matrix}{{LLR}_{i} \cong {\frac{1}{\sigma_{n}^{2}}\left( {{\min\limits_{\hat{s} \in S_{i}^{-}}{{r - {h\quad\hat{s}}}}^{2}} - {\min\limits_{\hat{s} \in S_{i}^{+}}{{r - {h\quad\hat{s}}}}^{2}}} \right)}} & \lbrack d\rbrack\end{matrix}$which is expressed in terms of Euclidean distances between the receivedsymbol r and the reconstructed candidate receive symbols hŝ. Forreceiver implementations that include an equalizer 306 (for example, seeFIG. 8), the LLR computation module 821 receives equalized symbols,which can be appreciated as leading to conceptually simplerrepresentation of LLR_(i).

Let {circumflex over (q)}=ŝσ_(q)/σ_(s) be ŝ normalized to fall on aninteger constellation grid, which will be discussed in detail withrespect to FIGS. 13 through 16. Further,[e]

|s |²

=σ_(s) ² and

|{circumflex over (q)}|²

=σ_(Q) ²Rewriting equation [d] using the normalized constellation provides:$\begin{matrix}{{LLR}_{i} = {{\frac{1}{\sigma_{n}^{2}}{\min\limits_{\hat{s} \in S_{i}^{-}}{{h\frac{\sigma_{S}}{\sigma_{Q}}\left( {{\frac{1}{h}\frac{\sigma_{Q}}{\sigma_{S}}r} - {\frac{\sigma_{Q}}{\sigma_{s}}\hat{s}}} \right)}}^{2}}} - {\frac{1}{\sigma_{n}^{2}}{\min\limits_{\hat{s} \in S_{i}^{+}}{{h\frac{\sigma_{S}}{\sigma_{Q}}\left( {{\frac{1}{h}\frac{\sigma_{Q}}{\sigma_{S}}r} - {\frac{\sigma_{Q}}{\sigma_{s}}\hat{s}}} \right)}}^{2}}}}} & \lbrack f\rbrack\end{matrix}$Collecting the common terms, equation [f] can be simplified further to:$\begin{matrix}{{{LLR}_{i} = {\frac{{h}^{2}}{\sigma_{n}^{2}}{\frac{\sigma_{S}^{2}}{\sigma_{Q}^{2}}\left\lbrack {{\min\limits_{\hat{q} \in Q_{i}^{-}}{\left( {p - \hat{q}} \right)}^{2}} - {\min\limits_{\hat{q} \in Q_{i}^{+}}{\left( {p - \hat{q}} \right)}^{2}}} \right\rbrack}}}{where}} & \lbrack g\rbrack \\{p = {{\frac{1}{h}\frac{\sigma_{Q}}{\sigma_{S}}r\quad{and}\quad\hat{q}} = {\frac{\sigma_{Q}}{\sigma_{S}}\hat{s}}}} & \lbrack h\rbrack\end{matrix}$and Q_(i) ⁻ is the set of normalized transmit symbols (that is,integer-valued symbols) where b_(i)=0, and Q_(i) ⁺ is the set ofnormalized transmit symbols where b_(i)=1. Because the scaling term of$\frac{{h}^{2}}{\sigma_{n}^{2}}\frac{\sigma_{\quad S}^{\quad 2}}{\sigma_{Q}^{2}}$is common, the scaled and normalized LLR from an equalizer 306 (whenpresent) equalizes the inbound symbol stream to the modulation typediscriminator 820), in which the formula is of the form: $\begin{matrix}{{\bigwedge_{i}{\equiv \frac{{LLR}_{i}}{\frac{{h}^{2}}{\sigma_{n}^{2}}\frac{\sigma_{\quad S}^{\quad 2}}{\sigma_{Q}^{2}}}}} = {{\min\limits_{\hat{q} \in Q_{i}^{-}}{\left( {p - \hat{q}} \right)}^{2}} - {\min\limits_{\hat{q} \in Q_{i}^{-}}{\left( {p - \hat{q}} \right)}^{2}}}} & \lbrack i\rbrack\end{matrix}$representing the nearest-neighbor squared Euclidean distances in aninteger constellation. As should be readily appreciated by those skilledin the art, the LLR computation module 821 may provide various LLRmetrics or methodologies, such as quantized version, and/or a scaledversion and/or a limited version of the LLR_(i) given in equation [d]and/or equation [i].

The modulation-type discrimination is made for robust modulation typeshaving improved transmission tolerance in view of adverse environmentalfactors (for example, signal interference, attenuation, etc.). Examplesof robust modulation-types are QPSK, BPSK, and rotated-BPSK. For thepresent invention, the modulation reference 836 is QPSK fordiscriminating with other robust modulation-types (e.g., BPSK,rotated-BPSK).

FIG. 13 is an illustration of the constellation of a modulationreference 836 plotted with respect to an in-phase axis (I) and aquadrature axis (Q). The modulation reference 836 provided is QPSK,which is a two-bit wide modulation and has a bit set equal to {b₁, b₀}with four points a, b, c, and d. QPSK is a form of modulation in which acarrier sends data symbols using a four phase modulation scheme toreflect one of four different two-bit wide data signals (00, 01, 10 and11). Those phases typically are 45, 135, 225, and 315 degrees. Thechange in phase from one symbol to the next encodes two bits per symbol.In QPSK, the four angles are usually out of phase by ninety degrees.

As shown, the four references a, b, c, and d have Cartesian coordinatesof: Point b₀ b₁ I-axis Q-axis a 1 1 1 J b 1 0 1 −j   c 0 0 −1   −j   d 01 1 JWith N symbols for each of the predetermined portions 520 or 521 the LLRcomputation module 821 computes an LLR for the bit 0 and bit 1 for eachof the N symbols, using either formula [i] (when an equalizer 306 ispresent) or formula [d] when an equalizer is not present. The cumulativeLLRs 826(1) and 826(2) are then formed by summing the absolute value ofLLR streams 822 for bit 0 and bit 1 of each of the N symbolsrespectively. $\begin{matrix}{{{Cumulative\_ LLR}\_ 224(1)} = {\sum\limits_{n}{{LLR}_{0,n}}}} & \lbrack j\rbrack\end{matrix}$and for bit b₁ can be represented as follows: $\begin{matrix}{{{Cumulative\_ LLR}\_ 224(2)} = {\sum\limits_{n}{{LLR}_{1,n}}}} & \lbrack k\rbrack\end{matrix}$Modulation type discrimination may be described with respect to theconstellation of the modulation reference, such as that described indetail with reference to FIGS. 14 through 16. For simplicity, thewireless channel is assumed to be “flat” or that the receiver includesan equalizer 306. Accordingly, the modulation type may be discriminatedby a comparison to the nearest neighbor in computing the LLRs as givenin the formula [i].

FIG. 14 is an example of a BPSK discrimination 840 with respect to anin-phase axis I versus a quadrature axis Q. As shown, a predeterminedportion symbol 606 of the received encoded signal is shown positioned inrespect to the modulation reference 227 such that the symbol represent aBPSK modulation orientation.

Based on a QPSK reference, the LLR module 221, with the LLR computation212, will generate two LLRs for the predetermined-portion symbol 852,one for bit bo and the other for bit b₁. The LLRs are computed based onformula [i] where {circumflex over (q)} can be any of the modulationreference 836 points a, b, c, and d. A cumulative LLR 826 for the Nsymbols of predetermined portion 520 or 521, results in whether thecumulative LLR 826(1) is greater than the cumulative LLR 826(2), in thatthe likelihood for bit b₀ of the predetermined portion is large whilethe likelihood for bit b₁ of the predetermined portion is small. Thismay be represented as: $\begin{matrix}{{{{Cumulative\_ LLR}\_ 224(1)} > {{Cumulative\_ LLR}\_ 224(2)}}{{or}\text{:}}} & \lbrack l\rbrack \\{{\sum\limits_{n}{{LLR}_{0,n}}} > {\sum\limits_{n}{{LLR}_{1,n}}}} & \lbrack m\rbrack\end{matrix}$Accordingly, the a posteriori likelihood is that the modulation typeoutput 830 is BPSK, where basic principle is to provide a carrier with aphase that is alternated between 0-degrees and 180-degrees, as needed,to convey digital information.

FIG. 15 is an example of a rotated-BPSK discrimination 842 with respectto an in-phase axis I versus a quadrature axis Q. As shown, apredetermined-portion sub-symbol 854 is positioned with respect to themodulation reference 836 such that the symbol represents a rotated-BPSKmodulation orientation.

The LLR computation module 821 generates two LLRs for thepredetermined-portion sub-symbol 854, one for bit b₀ and the other forbit b₁. The LLRs are computed based on the formula [i] where {circumflexover (q)} can be any of the modulation reference 836 points a, b, c, andd. A cumulative LLR 826 for N symbols of the predetermined portion showthat the cumulative LLR 826(1) is less than the cumulative LLR 826(2),in that the likelihood for bit b₀ of the predetermined portion 520 or521 is small while the likelihood for bit b₁ of the predeterminedportion 520 or 521 is large. This may be represented as: $\begin{matrix}{{{{Cumulative\_ LLR}\_ 224(1)} < {{Cumulative\_ LLR}\_ 224(2)}}{{or}\text{:}}} & \lbrack n\rbrack \\{{\sum\limits_{n}{{LLR}_{0,n}}} < {\sum\limits_{n}{{LLR}_{1,n}}}} & \lbrack o\rbrack\end{matrix}$Accordingly, the a posteriori likelihood is that the modulation typeoutput 830 is rotated-BPSK, where rotated BPSK provides a phase that isalternated between 90-degrees and 270 degrees, as needed, to conveydigital information.

FIG. 16 is an example of a QPSK discrimination 844 with respect to anin-phase axis I versus a quadrature axis Q. As shown, the predeterminedportion sub-symbol 856 of the received encoded signal is positioned withrespect to the modulation reference 836 such that the N symbols of thepredetermined portion 520 or 521 represent a QPSK modulationorientation.

With a QPSK modulation reference 836, the LLR computation module 821generates two LLRs for the predetermined-portion symbol 856, one for bitb₀ and the other for bit b₁. The LLRs are computed based on formula [i]where {circumflex over (q)} can be any of the modulation reference 836points a, b, c, and d. A cumulative LLR 826 for the N symbols of thepredetermined portion 520 or 521 show the cumulative LLR 826(1) beingsubstantially equivalent to the cumulative LLR 826(2). This may berepresented as: $\begin{matrix}{{{{Cumulative\_ LLR}\_ 224(1)} \approx {{Cumulative\_ LLR}\_ 224(2)}}{or}} & \lbrack p\rbrack \\{{\sum\limits_{n}{{LLR}_{0,n}}} \approx {\sum\limits_{n}{{LLR}_{1,n}}}} & \lbrack q\rbrack\end{matrix}$Accordingly, the a posteriori likelihood is that the modulation typeoutput 830 is QPSK.

FIG. 17 is a result table illustrating the operation functional state ofthe modulation-type discriminator 820 of FIG. 12. The result table 850includes three columns, a comparison results column 858, a cumulativeLLR column 860, and a modulation type column 862.

The table 850 is arranged for informational use in that it does not setout a mandated comparison sequence or order. For example, the magnitudedifferences shown in rows 854 and 856 are more readily discernible withrespect to the magnitude of the comparison difference of row 852. Itfollows then that if the conditions set out in rows 854 and 856 are notpresent, then the logical result is a favorable comparison result of row852. As should be readily appreciated by those skilled in the art, othercomparison methodologies may be used for arriving at a modulation-typeoutput decision. Also, for the example provided in FIG. 17, themodulation reference 836 is a QPSK signal reference such as thatillustrated in FIG. 13.

Accordingly, the cumulative LLRs 826(1) and 826(2) that the summingmodule 824 outputs to the discriminator module 828, are discriminated toproduce a modulation type output 830. With respect to row 852, afavorable result with respect to cumulative LLRs is provided when thefirst cumulative LLR 826(1) is substantially equivalent to the secondcumulative LLR 826(2). In other words, the modulation-type of the signalfield from the received encoded signal correlates to the modulationreference 836.

With respect to row 854, an unfavorable result exists when the firstcumulative LLR 826(1) is greater than the second cumulative LLR 826(2),scaled by a tolerance β, which indicates a BPSK modulation type. Thetolerance β accounts for signal variances from channel characteristics,receiver characteristics, et cetera. For example, a large number ofvariants are introduced through the transmission environment, the aposteriori likelihood can be made greater by placing the tolerance βgreater than “1.”

In the third row 856, a further unfavorable determination results whenfirst cumulative LLR 826(1) is less than the second cumulative LLR826(2) scaled by a tolerance β. In this instance, the modulation type830 for the predetermined portion is a rotated-BPSK. Again, for example,a large number of variants are introduced through the transmissionenvironment, the a posteriori likelihood can be made greater by placingthe tolerance β less than “1.”

FIG. 18 is a logic diagram illustrating a method 870 of discriminating amodulation type for decoding a signal field of an encoded signal in awireless communication system. Starting at step 872, the method 870proceeds to step 874 where a radio frequency receiver receives anencoded signal. At step 876, the radio generates at least a first LLRstream and a second LLR stream for each of a plurality of sub-symbolsfor a predetermined portion of the received encoded signal. The LLRstreams are based upon an m-bit wide modulation reference, where mrepresents the bit width of the modulation reference. Accordingly, thefirst LLR stream and the second LLR stream includes a plurality of LLRvalues. At step 878, the plurality of LLR values of the first LLR streamare summed to produce a first cumulative LLR, and at step 880 theplurality of LLR values of the second LLR stream are summed to produce asecond cumulative LLR. The radio discriminates the first cumulative LLRwith the second cumulative LLR to produce a discriminated modulationtype output at step 882. At step 884, the radio decodes the signal fieldbased on the discriminated modulation type output. With the capabilityto discriminate modulation types at a radio receiver via the method 870,a received encoded signal may have one of many frame types in which atransmitter may apply different modulation types based upon wirelesschannel conditions within a wireless communications network.

FIG. 19 is a logic diagram illustrating a method 882 to discriminate thecumulative LLRs of FIG. 18. At step 892, the radio receiverdiscriminates the modulation type by comparing the at least first andsecond cumulative LLR. At step 880, upon a favorable comparison of thefirst cumulative LLR with the second cumulative LLR, the discriminatedmodulation type is set to a first specified modulation type of aplurality of specified modulation types at step 882. At step 880, uponan unfavorable comparison of the first cumulative LLR with the secondcumulative LLR, the discriminated modulation type is set to one of asecond or a third specified modulation type at step 884. With themodulation type set, the method continues to step 884 of FIG. 18.

A radio receiver may further discriminate the modulation type of thereceived encoded signal of step 874 by the difference between themodulation types of the first cumulative LLR and the second cumulativeLLR. That is, when the first cumulative LLR is greater than the secondcumulative LLR, the discriminated modulation type may be set to thesecond specified modulation type. On the other hand, when the firstcumulative LLR is less than the second cumulative LLR, the discriminatedmodulation type may be set to the third specified modulation type.Accordingly, in the present example, the radio receiver may discriminatea modulation type of QPSK, BPSK, and rotated-BPSK modulations.

Another embodiment provides for discriminating the signalmodulation-type based upon a conjugation of the wireless channel. Theembodiment bases the discrimination upon a predetermined portion 520 and521 (see, for example, FIGS. 6 and 7) by processing a predeterminedportion of the inbound symbol stream 124, such as a preamble trainingsequence associated with a frame, through the nature or potentialcharacteristics of the inbound symbols. The received symbol stream isrepresented as:[r]r _(n) =h _(n) s _(n) +Z _(n)where r is the received symbol, h is the channel, s is the transmittedsymbol, z is the additive white Gaussian noise and the index n denotesthe n^(th) symbol of the predetermined portion. Multiplying r_(n) withthe conjugate of the wireless channel h_(n) (in which the ideal channelestimation is used for simplicity) gives:[s]V _(n)=Conj(h _(n))r _(n) =|h _(n)|² s _(n)+conj(h _(n))z _(n)where V_(n) is a complex symbol. A receiver processes the magnitudes ofthe real and imaginary portions of V_(n) from an inbound symbol stream124 to produce a discriminated modulation type output. The discriminatedmodulation type output indicates modulation types for the signal fieldsuch as BPSK-encoded, rotated BPSK-encoded, or QPSK-encoded.

For example, when the transmitted symbol s_(n) is BPSK-encoded, and whenthe signal-to-noise ratio (SNR) for the wireless channel is sufficientlylarge to minimize distortion of the corresponding constellationcoordinate for the transmitted symbol, then the absolute value, ormagnitude, of the real portion of conjugate V_(n) is much greater thanthe absolute value, or magnitude, of the portion of the conjugate V_(n).When the transmitted symbol s_(n) is rotated BPSK-encoded, and when thesignal-to-noise ratio (SNR) for the wireless channel is sufficientlylarge, then the absolute of the real portion of conjugate V_(n) is muchsmaller than the absolute of the imaginary portion of the conjugateV_(n). If the transmitted symbol s_(n) is QPSK-encoded, then theabsolute of the real part of V_(n) is approximate to the absolute of theimaginary portion of V_(n).

In yet another embodiment, the discriminator module 828 performs atri-state discrimination function based upon the wireless channelconjugate V_(n) to produce a modulation type output 830. The tri-stateresults include the possible values of {−1, 0, 1} based upon apredetermined portion 520 (or 521) of the inbound symbol stream 124. Thetri-state operation is presented as follows: $\begin{matrix}{\rho = {\frac{1}{\sum\limits_{n = 1}^{N}{h_{n}}^{2}}{\sum\limits_{n = 1}^{N}\left\lbrack {{{{Re}\left( V_{n} \right)}} - {{{Im}\left( V_{n} \right)}}} \right\rbrack}}} & \lbrack t\rbrack\end{matrix}$Accordingly, when ρ approximates “1,” then the transmitted symbol s_(n)is BPSK-encoded. When ρ approximates “−1,” then the transmitted symbols_(n) is rotated BPSK-encoded. And when ρ approximates “0,” then thetransmitted symbol s_(n) is QPSK-encoded.

FIG. 20 is a logic diagram illustrating a method 900 for decoding asignal field of an encoded signal in a wireless communication system.The decoding is based upon discriminating the signal modulation-typebased upon a conjugation of the wireless channel.

Starting at step 902, a receiver receives an encoded signal having apreamble training sequence associated with a frame, the preambletraining sequence including the signal field. At step 903, the receiverprocesses a plurality of sub-symbols of the received encoded signalassociated with the signal field to produce a stream having a realportion and an imaginary portion for each of the sub-symbols, each ofthe portions having a magnitude.

The receiver may process the plurality of sub-symbols by multiplying thereceived encoded signal with the conjugate of the wireless channel (inwhich the ideal channel estimation is used for simplicity). The resulthas real and imaginary portions, in which at step 908, for eachsub-symbol, the receiver discriminates the magnitude of the real portionwith the magnitude of the imaginary portion of the inbound symbol stream124 to produce a discriminated modulation type output, such asBPSK-encoded, rotated BPSK-encoded, or QPSK-encoded. At step 910, thereceiver decodes the signal field based upon the discriminatedmodulation type output. The process continues with subsequent frames byreturning to step 904.

As may be used herein, the terms “substantially” and “approximately”provides an industry-accepted tolerance for its corresponding termand/or relativity between items. Such an industry-accepted toleranceranges from less than one percent to fifty percent and corresponds to,but is not limited to, component values, integrated circuit processvariations, temperature variations, rise and fall times, and/or thermalnoise. Such relativity between items ranges from a difference of a fewpercent to magnitude differences. As may also be used herein, theterm(s) “coupled to” and/or “coupling” and/or includes direct couplingbetween items and/or indirect coupling between items via an interveningitem (e.g., an item includes, but is not limited to, a component, anelement, a circuit, and/or a module) where, for indirect coupling, theintervening item does not modify the information of a signal but mayadjust its current level, voltage level, and/or power level. As mayfurther be used herein, inferred coupling (i.e., where one element iscoupled to another element by inference) includes direct and indirectcoupling between two items in the same manner as “coupled to”. As mayeven further be used herein, the term “operable to” indicates that anitem includes one or more of power connections, input(s), output(s),etc., to perform one or more its corresponding functions and may furtherinclude inferred coupling to one or more other items. As may stillfurther be used herein, the term “associated with”, includes directand/or indirect coupling of separate items and/or one item beingembedded within another item. As may be used herein, the term “comparesfavorably”, indicates that a comparison between two or more items,signals, etc., provides a desired relationship. For example, when thedesired relationship is that signal 1 has a greater magnitude thansignal 2, a favorable comparison may be achieved when the magnitude ofsignal 1 is greater than that of signal 2 or when the magnitude ofsignal 2 is less than that of signal 1.

1. A method of discriminating a modulation type for decoding a signalfield of an encoded signal in a wireless communication system, themethod comprises: receiving the encoded signal having a preambletraining sequence associated with a frame, the preamble trainingsequence including the signal field; generating at least a firstlog-likelihood ratio (LLR) stream and a second LLR stream for each of aplurality of sub-symbols for a predetermined portion of the receivedencoded signal based upon an m-bit wide modulation reference, wherein mrepresents the bit width of the modulation reference, the first LLRstream and the second LLR stream includes a plurality of LLR values;summing the plurality of LLR values of the first LLR stream to produce afirst cumulative LLR; summing the plurality of LLR values of the secondLLR stream to produce a second cumulative LLR; discriminating the firstcumulative LLR with the second cumulative LLR to produce a discriminatedmodulation type output; and decoding the signal field based on thediscriminated modulation type output.
 2. The method of claim 1 whereinthe discriminating step further comprises: upon a favorable comparisonof the first cumulative LLR with the second cumulative LLR, setting thediscriminated modulation type to a first specified modulation type of aplurality of specified modulation types; and upon an unfavorablecomparison of the first cumulative LLR with the second cumulative LLR,setting the modulation type to one of a second or a third specifiedmodulation type.
 3. The method of claim 2 wherein the third specifiedmodulation type is a rotated second specified modulation type.
 4. Themethod of claim 2 wherein the setting of the discriminated modulationtype to one of the second or the third specified modulation typecomprises: when the first cumulative LLR is greater than the secondcumulative LLR, setting the discriminated modulation type to the secondspecified modulation type; and when the first cumulative LLR is lessthan the second cumulative LLR, setting the discriminated modulationtype to the third specified modulation type.
 5. The method of claim 1wherein the modulation reference is a QPSK modulation type.
 6. Themethod of claim 2 wherein the second specified modulation type is a BPSKmodulation type.
 7. The method of claim 2 wherein the third specifiedmodulation type is a rotated BPSK modulation type.
 8. The method ofclaim 1 wherein the predetermined portion is a signal field.
 9. Themethod claim 1 wherein the generating step further comprises: selectingthe predetermined portion based on a format from a plurality of formatsof the frame.
 10. A modulation-type discriminator for a radio frequencyreceiver comprises: a log-likelihood ratio (LLR) module operable toreceive a signal field of an encoded signal having a preamble trainingsequence associated with a frame, the LLR module operable to generate afirst and a second LLR stream for each of a plurality of sub-symbols fora predetermined portion of the received encoded signal based on atwo-bit wide modulation reference; a summing module disposed to receivethe first and the second LLR streams and operable to cumulatively thefirst LLR stream to produce a first cumulative LLR and the second LLRstream to produce a second cumulative LLR; and a discriminator moduleoperable to receive the first and the second cumulative LLR, and furtheroperable to compare each of the first and the second cumulative LLR toprovide a discriminated modulation type from a plurality of specifiedmodulation types.
 11. The modulation-type discriminator of claim 10,wherein the discriminator module is further operable to: upon afavorable comparison result that discriminates the received signal fieldas substantially equivalent to the modulation reference, setting thediscriminated modulation type to a first specified modulation type ofthe plurality of specified modulation types; and upon an unfavorablecomparison result that discriminates the received signal field as beingnon-equivalent to the modulation reference, setting the discriminatedmodulation type to one of a second or a third specified modulation typeof the plurality of specified modulation types.
 12. The modulation-typediscriminator of claim 11 wherein the discriminator module, upon anunfavorable comparison result, is further operable to: when the firstcumulative log likelihood ratio is greater than the second cumulativelog likelihood ratio, set the discriminated modulation type to thesecond specified modulation type; and when the first cumulative loglikelihood ratio is less than the second cumulative log likelihoodratio, set the discriminated modulation type to the third specifiedmodulation type.
 13. The modulation-type discriminator of claim 10wherein the modulation reference is a QPSK modulation type.
 14. Themodulation-type discriminator of claim 11 wherein the first specifiedmodulation type of the plurality of specified modulation types is a QPSKmodulation type.
 15. The modulation-type discriminator of claim 11wherein the second specified modulation type of the plurality ofspecified modulation types is a BPSK modulation type.
 16. Themodulation-type discriminator of claim 11 wherein the third specifiedmodulation type of the plurality of specified modulation types is arotated-BPSK modulation type.
 17. The modulation-type discriminator ofclaim 10 wherein the predetermined portion is a signal field.
 18. Themodulation-type discriminator of claim 10 wherein the predeterminedportion is based on a format from a plurality of formats for the frame.19. An integrated circuit radio transceiver comprises: transmit signalpath circuitry operable to transmit radio-frequency signals; receivesignal path circuitry operable to receive radio-frequency signals havinga preamble associated with a frame, the preamble having a signal field,the receive signal path circuitry includes modulation-type discriminatorcircuitry coupled to discriminate a signal field modulation type from apredetermined portion of a received radio-frequency signal, themodulation-type discriminator circuitry includes logic circuitry thatcomprises: a digital receiver processing module; and memory coupled tothe digital receiver processing module, wherein the memory storesoperational instructions that prompts the digital receiver processingmodule to: generate at least a first log-likelihood ratio (LLR)streamand a second LLR stream for each of a plurality of sub-symbols for apredetermined portion of the received encoded signal based upon an m-bitwide modulation reference, wherein m represents the bit width of themodulation reference, the first LLR stream and the second LLR streamincludes a plurality of LLR values; sum the plurality of LLR values ofthe first LLR stream to produce a first cumulative LLR; sum theplurality of LLR values of the second LLR stream to produce a secondcumulative LLR; discriminate the first cumulative LLR with the secondcumulative LLR to produce a discriminated modulation type output; anddecode the signal field based upon the discriminated modulation typeoutput.
 20. The integrated circuit radio transceiver of claim 19 whereinthe discrimination of the modulation type by the digital receiverprocessor further comprises: upon a favorable comparison result thatdiscriminates the signal field of the received radio-frequency signal assubstantially equivalent to the two-bit wide modulation reference,setting the discriminated modulation type to a first specifiedmodulation type of the plurality of specified modulation types; and uponan unfavorable comparison result that discriminates the signal field ofthe received radio-frequency signal as being non-equivalent to thetwo-bit wide modulation reference, setting the discriminated modulationtype to one of a second or a third specified modulation type of theplurality of specified modulation types.
 21. The integrated circuitradio transceiver of claim 20 wherein setting the modulation type to oneof a second or a third specified modulation type of the plurality ofspecified modulation types by the digital receiver processor furthercomprises: when the first cumulative log likelihood ratio is greaterthan the second cumulative log likelihood ratio, setting thediscriminated modulation type to the second first specified modulationtype; and when the first cumulative log likelihood ratio is less thanthe second cumulative log likelihood ratio, setting the discriminatedmodulation type to the third specified modulation type.
 22. Theintegrated circuit radio transceiver of claim 19 wherein the modulationreference is a QPSK modulation type.
 23. The integrated circuit radiotransceiver of claim 20 wherein the first specified modulation type ofthe plurality of specified modulation types is a QPSK modulation type.24. The integrated circuit radio transceiver of claim 20 wherein thesecond specified modulation type of the plurality of specifiedmodulation types is a BPSK modulation type.
 25. The modulation-typediscriminator of claim 19 wherein the predetermined portion is a signalfield.
 26. A method of discriminating a modulation type for decoding asignal field of an encoded signal in a wireless communication system,the method comprises: receiving the encoded signal having a preambletraining sequence associated with a frame, the preamble trainingsequence including the signal field; processing a plurality ofsub-symbols of the received encoded signal associated with the signalfield to produce a stream having a real portion and an imaginary portionfor each of the sub-symbols, each of the portions having a magnitude;for each sub-symbol, discriminating the magnitude of the real portionwith the magnitude of the imaginary portion to produce a discriminatedmodulation type output; and decoding the signal field based on thediscriminated modulation type output.
 27. The method of claim 26 whereinprocessing the plurality of sub-symbols further comprises: multiplyingthe received encoded signal with the conjugate of a channel estimate.28. The method of claim 26, wherein when the magnitude of the realportion and the imaginary portion approximate each other, thediscriminated modulation type output is a first modulation type.
 29. Themethod of claim 28, wherein when the magnitude of the real portion andthe imaginary portion are not approximate to each other, thediscriminated modulation type output is one of a second or a thirdmodulation type.
 30. The method of claim 29, wherein: when the magnitudeof the real portion is greater than that of the imaginary portion, thediscriminated modulation type output is the second specified modulationtype; and when the magnitude of the real portion is less than that ofthe imaginary portion, the discriminated modulation type output is thethird specified modulation type.
 31. The method of claim 29 wherein thefirst modulation type is a QPSK modulation type.
 32. The method of claim31 wherein the second modulation type is a BPSK modulation type.
 33. Themethod of claim 32 wherein the third specified modulation type is arotated BPSK modulation type.